Even if a dedicated comparator can be a little cheaper than a full adder, all CPUs already have full adders/subtractors, so all the comparisons are done by subtraction in the same adder/subtractor.
So your recommended sequence has 4 additions done in the adder/subtractor of the ALU, because all comparisons, including the compare-and-branch instructions, count as additions, from the point-of-view of the energy consumption and execution time.
> So your recommended sequence has 4 additions done in the adder/subtractor of the ALU, because all comparisons, including the compare-and-branch instructions, count as additions, from the point-of-view of the energy consumption and execution time.
For the signed overflow case, with compile-time unknown value added, if the processor doesn't do anything fancy to elide the recommended sequence (fusion or substitution of operation) only. Not for the other two cases, and not with fusion.
